Move authmate to neofs-s3-gw

[masterSplinter01]

Closes #46

Moved authmate repository to neofs-s3-gw.

Renamed the package s3 and the file s3.go from authmate-repo to "authmate" to authmate.go.

Created new folders and placed source files this way:

1. authmate/authmate.go
2. cmd/authmate/main.go

Added building of bins to Makefile. Now bin file has name 'neofs-authmate'.

Binary files of neofs-authmate was not added to dockerfile/docker image etc.

[roman-khimov]

Or you can just squash 137e690 and dae6936. Otherwise it's a bit noisy here, though other commits are nice.

Have you tried make lint on it?

And is it literally [nspcc-dev#46] in commit headings? Maybe [#46] is enough?

[masterSplinter01]

Sorry, squashed noisy commits.

[roman-khimov]

And is it literally [#46] in commit headings? Maybe [#46] is enough?

As I've suspected it's GitHub playing its autoreplace tricks, NM.

[roman-khimov]

Please fix linters and it'd be good to merge:

authmate/authmate.go:186:72  godot     Comment should end in a period
cmd/authmate/main.go:35:20   godot     Comment should end in a period
authmate/authmate.go:30:6    golint    exported type `Agent` should have comment or be unexported
authmate/authmate.go:35:1    golint    exported function `New` should have comment or be unexported
authmate/authmate.go:40:2    golint    exported type `IssueSecretOptions` should have comment or be unexported
authmate/authmate.go:49:2    golint    exported type `ObtainSecretOptions` should have comment or be unexported
authmate/authmate.go:91:1    golint    exported method `Agent.IssueSecret` should have comment or be unexported
authmate/authmate.go:141:1   golint    exported method `Agent.ObtainSecret` should have comment or be unexported
cmd/authmate/main.go:130:33  gosimple  S1019: should use make([]hcs.Credentials, count) instead
cmd/authmate/main.go:166:33  gosimple  S1019: should use make([]gateKey, len(csl)) instead
make: *** [Makefile:95: lint] Ошибка 1

[masterSplinter01]

Added new changes via linter messages. Could you please check them, especially new comments?